The spraying of various liquids on agricultural fields, for example, fertilizers, weed killers, etc., is common with respect to most types of farming and for most types of crops. The liquids tend to be expensive. They can also be caustic or otherwise pose some danger, not only to implement operators, but to plant life for which the liquids may not be designed. It is necessary to carefully control spraying. In this regard, it is important to fully clean the spraying implement when switching from one liquid to be sprayed to another. In particular, there has been the problem that remnants of the liquid last sprayed remain in the system when a new liquid to be sprayed is loaded in the system.